1. Field of the Invention
The present invention relates to an image display apparatus capable of storing and displaying an image.
2. Description of Related Art
There is an image display apparatus arranged to convert a negative image recorded on a developed film into an electrical signal by means of a CCD camera and display an image represented by the electrical signal on a CRT or a liquid crystal display. There is also an image display apparatus arranged to optically project an image from a developed positive film onto a dedicated screen.
However, the apparatus using a CCD camera is not suited to the applications of displaying silver-halide photographs, because the density of pixels of a display or a CCD which serves as image pickup means is coarse to such an extent that, for example, the face of a photographed person cannot be identified. In addition, the amount of light transmitted through a developed negative film is less than 10% for each average scene, and if such a negative image is to be magnified and projected, the necessary amount of light becomes excessively large. This leads to the problem that an image display apparatus of excessively large size is needed.
On the other hand, it is not easy for general users to use an image display apparatus for positive film, because they are forced to carefully select photographic conditions during photography with positive film. Furthermore, as compared with negative film, positive film is not favorable to general users in terms of cost and time, because, for example, positive film needs a time-consuming development process and the printing of a photographed image from a desired frame requires an extra time-consuming process.
It has been proposed to provide an image display apparatus which is capable of solving the above-described disadvantages and is suited to photograph stands, electronic albums or the like. This type of image display apparatus is arranged to optically project a negative image on a display screen, and in such image display apparatus, a spatial light modulator (hereinafter referred to as the SLM) which can reverse a negative image is used as a screen so that an image recorded on negative film which is commonly used by general users can be easily viewed. In addition, in such image display apparatus, a ferroelectric liquid crystal (hereinafter referred to as the FLC) having a memory function is used as the liquid crystal of the SLM, and a negative image is instantaneously written to the SLM by using a flash device of the type which is used in cameras or the like. A user can observe the written image by means of illumination with reading light.
FIGS. 13 and 14 show the previously proposed image display apparatus. FIG. 13 shows the entire construction of an image display apparatus 201. In the apparatus shown in FIG. 13, a developed negative film 203 which is drawn from a film cartridge is indexed to an aperture position (which is shown in FIG. 13) on a frame-by-frame basis by a known film winding mechanism. A diffuser 204 which has milk white diffuses light emitted from a flash device 205 (to be described later) and uniformly illuminates the negative film 203.
The flash device 205 is of a type similar to that used in cameras or the like, and includes a xenon tube, a reflector, a light emission circuit and the like and emits light in response to a trigger signal supplied from a known microprocessor (not shown).
An orange base color eliminating filter 206 performs the function of eliminating the color of an orange base from a negative image, and is composed of an optical filter having blue which is the complementary color of orange.
A projecting lens 207 projects a negative image recorded on the negative film 203 onto an SLM 209 (to be described later) via a reflecting mirror 208 at a predetermined magnification.
The SLM 209 includes a color filter of pure colors or complementary colors, an ITO (indium tin oxide) layer which constitutes one transparent electrode, a photoconductor layer made from an organic semiconductor film or the like, a liquid crystal layer made of a ferroelectric liquid crystal (FLC) or the like, an alignment film, an ITO layer which constitutes another transparent electrode, opposed glasses, and opposed polarizers. These layers are stacked one on another in such a manner that the layers are sandwiched between the opposed glasses and the opposed polarizers. If an image is projected onto the back surface of the SLiM 209 with a predetermined voltage being applied across the transparent electrodes, the image is stored in the liquid crystal layer, and the stored image is held even after the application of the predetermined voltage has been stopped. Then, if the back surface of the SLM 209 is illuminated with a reading illumination lamp 212, a user can view the image stored in the liquid crystal layer on the front surface of the SLM 209. The reading illumination lamp 212 is a straight tube lamp of the type which is widely used in flat displays or the like.
The operation of the image display apparatus 201 will be described below with reference to the flowchart of FIG. 14. If a film cartridge which accommodates the negative film 203 having images which the user desires to view is mounted in the image display apparatus 201 by the user (S501), the image display apparatus 201 performs a thrust operation for feeding the negative film 203 from the film cartridge, and positions the first frame of the negative film 203 at the aperture position of the image display apparatus 201 and stops the thrust operation (S502). In this state, the image display apparatus 201 enters a standby mode for waiting for a signal to be sent from any of individual switches (not shown) (S503).
In this state, if the image display apparatus 201 receives a signal indicative of an instruction to advance the negative film 203 up to an intermediate frame, for example, from a remote controller (S504), the image display apparatus 201 positions a specified frame at the aperture position (S505) and enters a standby mode for waiting for a command to display the image of the specified frame (S506).
In this state, if the image display apparatus 201 receives a display command from the user (S507), the image display apparatus 201 turns on a power source switch (not shown) in order to erase the displayed image of the previous frame (S508), and turns on the reading illumination lamp 212 (S509), and then applies a reverse electric field to that applied during writing, to the electrodes of the SLM 209 (S510). Thus, the FLC molecules of all the cells of the SLM 209 are reversed and brought to a laterally oriented state, whereby the FLC is brought to its neutral state (S511). After enough time to bring the FLC molecules of all the cells to the laterally oriented state has elapsed, the image display apparatus 201 turns off the power source switch to turn off the reading illumination lamp 212 (S512 and S513).
Then, the image display apparatus 201 performs the operation of writing a new image. It is assumed that the image display apparatus 201 is placed on the top of a desk in an office or on a shelf in a home and is illuminated with a brightness of approximately several hundred lux. The external light is reduced to approximately half in intensity by passing through the polarizer and the liquid crystal layer of the SLM 209, and then enters the photoconductor layer. However, if the SLM 209 is not energized, no electric field is not applied to the ITO films, and hence the FLC does not respond.
In this state, if the image display apparatus 201 turns on the power source switch (S514), a forward electric field which is required to write an image is applied to the ITO films by the power source (S515). Then, the image display apparatus 201 causes the flash device 205 to emit flash light (S516) and projects the image recorded on the negative film 203 onto the SLM 209 by means of the flash light so that the SLM 209 memorizes the projected image.
This writing operation, which is performed with the SLM 209 being exposed to external light in the above-described manner, must be rapidly performed under conditions which allow projected light to exhibit a prescribed S/N ratio with respect to external light. However, since the flash emission performed in Step S516 comes to an end in approximately 500 .mu.sec, the operation of turning on the power source switch in Step S515 is also performed in a time of approximately the same length and at approximately the same timing. After the completion of the flash emission, the image display apparatus 201 immediately turns off the power source switch to cut the electric field (S517). After that, the image display apparatus 201 turns on the reading illumination lamp 212 so that the user can view the image stored in the SLM 209, by means of transmitted illumination (S518).
After that, the image display apparatus 201 enters the standby mode for receiving the next command (S503), and the user can continue to view the image stored in the SLM 209 which has been set in the above-described operation.
In accordance with the above-described sequence, it is possible to write an image to the SLM 209 by supplying electrical potential to the photoconductor layer of the SLM 209 in synchronism with the flash emission of the flash device 205 for only a slight period of time.
As another image display apparatus, the still image display shown in FIGS. 15 to 17 has been proposed. The following description will focus on points which differ from the above-described features of the image display apparatus 201. As shown in FIGS. 15 to 17, a still image display 301 includes various parts which will be described later, in built-in form. A scanner unit 310 is provided with a cartridge chamber (not shown), and a film cartridge 302 is mounted in the cartridge chamber. A negative film 303 is fed out from the film cartridge 302 by a known film transporting mechanism, and a photographed-image frame 303a specified by a user is fed into the optical path of a line CCD 316 which will be described later.
A scanning illuminating light source 314 generally includes a three-wavelength tube (a fluorescent tube of the type whose R, G and B wavelengths are accurately balanced) 314a, a reflector 314b, and a diffuser located at a position which is invisible in FIG. 15. The scanning illuminating light source 314 is disposed at a position where it can be kept in approximately close contact with the negative film 303.
A projecting lens 315 serves to project an image recorded on the negative film 303 onto the line CCD 316 as an image of reduced size, and includes in built-in form predetermined mechanisms (not shown) such as a known autofocus mechanism and an iris device which is an exposure adjustment mechanism.
The line CCD 316 has three R, G and B lines. The information outputted from the respective R, G and B lines is inputted to A/D converters 317 via shift registers, and the output information is converted into digital information by the respective A/D converters 317. After that, the digital information is inputted to a mixing circuit 318, and the output from the mixing circuit 318 is inputted to a laser driving circuit 319. The output of the laser driving circuit 319 is connected to a semiconductor laser 322 (which will be described later) to drive the semiconductor laser 322.
The semiconductor laser 322 serves to emit near infrared light, and includes an erasing laser 322a for erasing an old image which is previously written to an SLM 309 and a writing laser 322b for writing image data which is newly sent from the scanner unit 310.
In the present still image display, the erasure of an old image from the SLM 309 and the writing of a new image to the SLM 309 are performed by a so-called wipe change-over method which causes the boundary between the old and new images to apparently move over the screen. Specifically, the reverse electric field to that applied during the writing of the old image is applied to the patterned portion of each of the ITO films that is several to some tens of lines previous to the new image to be written, and the infrared light of the erasing laser 322a is made to illuminate on a D.C. basis to create a uniform pre-writing state of liquid crystal. Accordingly, if an erasing operation and a writing operation are to be performed with different semiconductor lasers at the same time, it is necessary to apply both plus and minus potentials relative to a common potential to the patterned ITO films, for example, -30 V for an erasing side and +30 V for a writing side with respect to 0 V for a common side (a non-patterned side). At this time, an electric field (an electric field parallel to the FLC) also occurs between -30 V and +30 V, but, as described previously, in order to prevent this electric field from adversely affecting erasing or writing, writing and erasing are performed not between adjacent patterns but between patterns distant from each other by a predetermined amount. Thus, an improvement in S/N ratio is achieved.
Incidentally, since the operation of actually erasing an old image and writing a new image is performed in a portion which is not exposed to external light by being covered with a light blocking plate 328b (to be described later), the user feels that the old image is wiped off the screen by the new image at a position corresponding to the light blocking plate 328b which is passing over the SLM 309.
A first positive lens unit 323 serves to approximately focus the laser light emitted from the laser 322, on a polygonal surface of a polygonal mirror 324. The polygonal mirror 324 is rotatably supported at a shaft 324a by a support mechanism (not shown) and has an external shape having an octahedral mirror surface.
A projecting lens 325 serves to project an image reflected from the polygonal mirror 324, onto the SLM 309, and focuses an image transmitted by the laser 322, on the photoconductor layer of the SLM 309 in accordance with an optical path which passes through a total reflection prism 331 and a total reflection mirror 332.
The rotation of the output shaft of a stepping motor 326 is transmitted to a first helicoid screw shaft 327 which is shown in detail in FIG. 16, thereby causing the first helicoid screw shaft 327 to turn on its axis. Thus, the light blocking plate 328b, which is engaged with a first female helicoid 328 meshed with the helicoid portion of the first helicoid screw shaft 327 and is fitted in a guide groove (not shown) formed in the still image display 301, travels along the top of the SLM 309 in the direction of the corresponding arrow shown in FIG. 17.
The first helicoid screw shaft 327 integrally has a connecting gear portion 327a. The connecting gear portion 327a is meshed with a gear portion 329a of a second helicoid shaft 329 which will be described later, and transmits the rotational driving force of the stepping motor 326 to the second helicoid shaft 329. The second helicoid shaft 329 is rotatably supported on the still image display 301 by a guide member (not shown), and a second female helicoid 330 is screw-connected to the helicoid portion of the second helicoid shaft 329. Accordingly, if the rotation of the stepping motor 326 is transmitted to the second helicoid shaft 329 via the gear portions 327a and 329a, the second female helicoid 330 travels along the bottom of the SLM 309 in the direction of the corresponding arrow shown in FIG. 17.
The leads of the respective threads of the first helicoid screw shaft 327 and the second helicoid shaft 329 are selected to be 2:1 so that as the first female helicoid 328 travels by one stroke, the second female helicoid 330 travels by a half stroke. Accordingly, the optical path length of laser light from the projecting lens 325 for focusing an image on the SLM 309 to the SLM 309 is approximately constant no matter where in the SLM 309 an image is to be written.
The second female helicoid 330 is provided with a prism support portion 330a which supports the triangular prism 331. As shown in FIG. 17, when laser light which has been reflected from the polygonal mirror 324 and passed through the projecting lens 325 enters the triangular prism 331, the triangular prism 331 reflects the laser light twice in its interior to change the direction of the laser light by 180.degree., and emits the laser light toward the reflection mirror 332. The reflection mirror 332 reflects the laser light to change the direction thereof by 90.degree., and focuses the laser light on the photoconductor layer of the SLM 309.
The reflection mirror 332 is supported by a support portion (not shown) provided on the first female helicoid 328, and travels integrally with the first female helicoid 328. Accordingly, even if the triangular prism 331 and the reflection mirror 332 respectively travel to the positions 331' and 332' shown in FIG. 17 by the driving force of the stepping motor 326 together with the light blocking plate 328b, the optical path length from the projecting lens 325 to the SLM 309 does not change, as described previously.
The light blocking plate 328b also serves the function of preventing external light from entering the photoconductor layer to which an electric field is applied, through the color filter part and the FLC of the SLM 309 when the laser 322 is erasing an old image or writing a new image.
A detection pattern 341 is used for outputting position information relative to the stripe-shaped ITO films of the SLM 309, and a known photosensor, which is opposed to the detection pattern 341, outputs pulse signals in a pattern corresponding to individual positions. Through these pulse signals, it is possible to detect positions illuminated with laser light outputted from the erasing laser 322a and the writing laser 322b, respectively, so that, by controlling the switching timing of each of the stripe-shaped ITO films, it is possible to apply an electric field in such a manner that the electric field is reversed each time an erasing operation and a writing operation are switched over therebetween.
An external data input terminal 342 is provided for receiving digital image data from the outside, such as CD-ROM data which is inputted via a personal computer (not shown), and the digital image data is inputted to an external data processing circuit 344. The external data processing circuit 344 converts the digital image data into optimum image data which can be written to and displayed on the SLM 309, and outputs the obtained image data to the mixing circuit 318 so that the laser 322 can be made to perform erasure of an old image and writing of a new image.
A backlight 343 includes a light source made of a three-wavelength fluorescent lamp or the like, and a known reflection light guide plate. This backlight 343 is turned on when a user is to view a written image after an image has been written to the SLM 309, and provides the user with an image illuminated with good backlight illumination.
However, in the previously described image display apparatus 201, since the writing of an image is performed with the SLM remaining exposed to external light, if the influence of external light which serves as noise is to be eliminated or a clear image is to be recorded, it is necessary to cause the flash device 205 to emit a large amount of writing light, i.e., a flash device of large size is needed as the flash device 205. In addition, since it is necessary to reduce the F number of the projecting lens 207, the lens diameter of a projecting optical system becomes large.
On the other hand, the above-described still image display 301, which is arranged to sequentially write an image to the SLM 309 in a form corresponding to the stripe-shaped ITO films, has the disadvantage that the still image display 301 requires a longer writing time than the image display apparatus 201. In addition, since the still image display 301 has the structure in which the light blocking plate 328b and the triangular prism 331 as well as the reflection mirror 332 are moved on the opposite sides of the SLM 309 according to the operation of writing an image, a mechanical structure associated with the SLM 309 is complicated.